Some disorders of the nervous system may be traced to particular portions of the brain. For example, Epilepsy is a nervous system disorder that can cause seizures due to abnormal electrical activity in a particular portion of the brain. Epilepsy affects approximately 50,000 to 100,000 people per year in the United States and is known to affect people of all age groups.
The abnormal electrical activity that occurs in the brain during an Epileptic seizure may be focused in the different portions of the brain depending upon the patient. As such, a patient's brain may be “mapped” to determine a particular portion of the brain that requires treatment. The mapping process may be accomplished using electroencephalogram (EEG) sensors placed on the outside of the patient's scalp, using magnetic resonance imaging (MRI) technique, or using electrocorticography (ECoG) electrodes placed on the outside of the brain through an opening formed in the patient's cranium. In general, the noninvasive methods of mapping the brain provide limited resolution compared to the more invasive methods that require access to the brain through a opening formed in the cranium, yet these invasive methods are often associated with a prolonged recovery period and an increased risk of morbidity.
Epilepsy and some other nervous system disorders can be treated with drug therapy or surgery. In many cases, the drugs are not fully effective for purposes of treating the disorder (e.g., epileptic seizures may still occur even with the treatment of drug therapy). Also, some of the drugs used to treat the nervous system disorder may have harmful or undesirable side effects.
Surgical treatment for Epilepsy and other nervous system disorders typically requires a surgeon to cut an opening in the patient's cranium. After the targeted area has been determined (e.g., using a mapping technique), the surgeon may remove the targeted brain tissue through the opening formed in the patient's cranium. Alternatively or in addition, the surgeon may insert electrodes through the opening in the patient's cranium into the targeted brain tissue to provide electrical stimulation to that area of the brain. For example, deep brain stimulation (DBS) is a technique, conventionally used to treat Parkinson's Disease and other nervous system disorders, in which the stimulation electrode is advanced through the opening in the patient's cranium to the thalamus or other area deep in the brain. These surgical techniques may be significantly invasive (e.g., requires an opening formed in the patient's cranium or requires access to the brain via the cerebrospinal fluid), which typically results in prolonged recovery times and, in some circumstances, an increased risk of morbidity.